Learning how to start and control fire changed human evolution. But humanity did not change fire until the Industrial Revolution.

For hundreds of thousands of years, using fire always meant an open flame. Much later, someone realized that the steam from boiling water—if confined—had power to make things move. With steam engines we harnessed fire’s power to work for us. Then, when we placed the combustion directly inside an engine, we almost literally set the world on fire.

Fire-power vastly extended our reach into the soils, the forests, the skies, and the seas. It allowed us to literally move mountains (or chop their tops off) to get at more fuel or minerals locked deep within the earth, slice down gigantic trees in a few minutes, and to send the nets of fishing fleets deep within the seas. Harnessed fire allowed construction, destruction, and transport at a scale and speed unimagined before 1800.

Since first becoming human, we have mainly been burning things to harness energy. To become fully human we’ll have to fully come out of the cave, quench the fires, and harness non-burning energy. But until then there is this problem: burning things—like coal, gas, oil,and wood—releases carbon dioxide.

Back in 1956, Roger Revelle and Hans Suess started measuring the air’s carbon dioxide to get “a clearer understanding of the probable climatic effects.” And that’s what they got.

Just to clarify, the greenhouse effect—caused mainly by the heat-blanket properties of water vapor, with an assist from carbon dioxide and other “greenhouse” gases—is natural and crucial; it prevents Earth from looking like a snowball. The concern is over how much additional heat heat-trapping gases will trap. Human-caused greenhouse gases have actually reversed a long, slow natural cooling. But we now have too much of a good thing.

There’s a third more carbon dioxide in the air than at the start of the Industrial Revolution. That’s an incredible change to the atmosphere. We did that, and we continue doing that every moment. The current carbon dioxide concentration is higher than it’s been for several million years; it’s rising 100 times faster than any time in the past 650,000 years. The planet has survived much higher greenhouse gas concentrations. Civilization hasn’t.

Our species invented agriculture about 10,000 years ago; writing and towns are about 5,000 years old. All of civilization and agriculture developed have existed inside a relatively stable atmosphere, and rather stable weather. Playing “I dare you” with the planet is not a game we’re good at bluffing.

Stabilizing climate requires that the world cut greenhouse gases 80 percent by 2050. But unlike the payoff of improving, say, sewers, cutting emissions won’t actually stabilize climate for perhaps another 50 years, because the planet will continue adjusting to gas already out of the bottle.

Doubling carbon dioxide—expected by between 2050 and 2080 unless we quench the fires—would create a roughly 5º F (2.75 º C) planetary-average warming. If we let that happen, we’ll hand our kids a different planet, far outside the range that any humans ever experienced, with no return possible within any foreseeable future generation. So it’s our children’s world we’re mainly talking about.

Some of what will happen next is already starting to happen now to people, to coral reefs, and to agriculture. Corals are “bleaching” and dying when water gets too hot. They are bathed in water that is increasing in acidity and its ability to corrode reefs. What happens to reefs will of course affect the food people can get from reefs. But warming will also affect the food people can grow on farms.

Climate change is the biggest umbrella issue of our lives, and likely the defining issue of our children’s lives, because it crowds into one crowded elevator our environment, conservation of nature, human health, the prospects for agriculture, international stability, national security, and of course energy policy and energy technology.

There’s a third more carbon dioxide: Intergovernmental Panel on Climate Change, 2001, The Scientific Basis; Contribution Of Working Group I To The Third Assessment Report Of The Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, New York. 100 times faster: Fabry, V. J., et al., 2008, “Impacts Of Ocean Acidification On Marine Fauna And Ecosystem Processes,” International Council for the Exploration of the Sea Journal of Marine Science 65: 414–432. Also: Royal Society, 2005, Ocean Acidification Due To Increasing Atmospheric Carbon Dioxide, Policy Document 12/05, The Royal Society, London, 60 pp.

Thanks for the sound and clear tutorial. Someone said we borrow the Earth from our children and we’re not doing a good job of returning it in its original, or even close, condition. We’re not getting the security deposit back this time. But seriously, climate change has to be the single greatest challenge facing humanity ever. The “smaller” issues of say regional biodiversity loss or a blight on watermelons — both important — pale in comparison to the global reach and comprehensive impact climate change will have on everything. Climate change will show us how everything is connected, and hopefully we can win back the Earth we all know.